Characteristics and Dynamics of Salmonella Contamination along the Coast of Agadir,Morocco

The occurrence of Salmonella enterica in the environment of tropical and desert regions has remained largely uninvestigated in many areas of the world, including Africa. In the present study, we investigated the presence of Salmonella spp. along 122 km of the coastline of Agadir (southern Morocco) in relation to environmental parameters. A total of 801 samples of seawater (243), marine sediment (279), and mussels (279) were collected from six sites between July 2004 and May 2008. The overall prevalence of Salmonella spp. was 7.1%, with the highest occurrence in mussels (10%), followed by sediment (6.8%) and seawater (4.1%). Only three serotypes were identified among the 57 Salmonella sp. strains isolated. S. enterica serotype Blockley represented 43.8% of all Salmonella strains and was identified in mussel and sediment samples. S. enterica serotype Kentucky (29.8%) was found almost exclusively in mussels, whereas S. enterica serotype Senftenberg (26.3%) was detected in sediment and seawater. Statistical analysis using generalized additive models identified seawater temperature, environmental temperature, rainfall, and solar radiation as significant factors associated with the presence of Salmonella. Rainfall was the only variable showing a linear positive effect on the presence of Salmonella in the sea, whereas the remaining variables showed more complex nonlinear effects. Twenty-eight (49.1%) Salmonella isolates displayed resistance to ampicillin (22 isolates), nalidixic acid (9 isolates), sulfonamide compounds (2 isolates), and tetracycline (1 isolate), with six of these isolates displaying multiple resistance to two of these antimicrobial agents. Pulsed-field gel electrophoresis analysis revealed homogenous restriction patterns within each serotype that were uncorrelated with the resistance pattern profiles.Salmonella enterica bacteria are one of the most frequent causes of food-borne infections transmitted to humans, mainly from animal products (9). In addition to health concerns, the presence of Salmonella contamination in the food chain has serious economic consequences related to the costs of medical care and lost productivity (36). Thus, studies aimed at examining the capacity of Salmonella spp. to survive in different habitats are critical for controlling contamination and understanding the routes of colonization of new hosts (40).Salmonella bacteria display a high degree of resistance to a large variety of stress factors, which provides them with an enhanced capacity to persist in changing environments (40). However, the persistence of the organism outside of the host is not uniform among the different serogroups (3, 4, 13, 24, 32, 34). About 50 of the more than 2,500 different serotypes of Salmonella included in the current classification scheme (29) are dominantly identified in human and animal sources (34). Information about groups that predominate in a given environment and their relationship to potential human or animal origins remains scarce. In recent years, some studies carried out in aquatic environments have provided new insights into the ecological preferences of different Salmonella serogroups in these environments. These studies have revealed the presence of specific patterns of contamination in different geographical areas in association with environmental and oceanographic variables (13, 24, 32) and have identified major factors and conditions that favor the presence of the contaminating bacteria. Identification of the different Salmonella strains present in the environment at serotype level is an essential preliminary step in discriminating potentially clinically important strains among the Salmonella present in contaminated areas, providing invaluable information about the nature of the contamination and allowing the inference of potential routes of dissemination through microbial source tracking (31). All of this information is critical for an improved assessment of the potential risks to public health associated with Salmonella and for the evaluation of the ecological preferences of the diverse and heterogeneous group of organisms which comprise the genus Salmonella (26).The lack of information regarding the epidemiology, contamination, and potential routes of transmission of Salmonella is of particular concern in many regions of the world, such as Africa and Central America, where gastrointestinal diseases continue to be a major cause of illness, primarily due to poor sanitary conditions and nutritional deficiencies. In the present study, we investigated the dynamics of Salmonella contamination in the coastal areas of Agadir, a populous region of southern Morocco where shellfish production and maritime tourism are important to the local economy. Information concerning the biological characteristics of the isolates was correlated with environmental data in order to evaluate the climatic conditions that favor contamination of this region by this pathogen and to identify the potential sources of contamination.